The present invention relates to a method for controlling a combined lathe apparatus, a combined lathe apparatus, a turning tool holder, a blade position registering apparatus, and a blade position detecting apparatus.
The basic design concepts for combined lathe apparatuses include the following 1) to 3).
These are the most important points which should be taken into consideration at the time of design.
1) The operator can come close to a workpiece and the tool headstock, which is easy to use.
2) The space for installing the machine tool within a factory is small.
3) Chips can be smoothly discharged and the chips are easy to be processed.
Thus, as shown in FIGS. 12(A) to 12(C), apparatuses having a moveable body 420, which is inclined by a predetermined angle θ relative to the horizontal line, have been used as a combined lathe apparatus having an automatic tool replacing apparatus. In general, the predetermined angle θ is 45°, 60°, or 90°. The moveable body 420 is placed above a bed 410 and a tool headstock 400 which is moveable along the X axis is provided on the moveable body 420. In the example in FIG. 12(A), the moveable body 420 moves along the horizontal line Yt and the tool headstock 400 moves along the X axis which makes a predetermined angle θ with respect to the horizontal line Yt. The horizontal line Yt is a straight line included in the horizontal plane and the X-Y plane.
In the example in FIG. 12(B), the moveable body 420 moves along the Y axis and the tool headstock 400 moves along the X axis which makes the predetermined angle θ with respect to the horizontal line Yt. In the example in FIG. 12(C), the moveable body 420 moves along the Y axis (horizontal line Yt) and the tool headstock 400 moves along the X axis which is perpendicular to the horizontal line Yt.
In this type of combined lathe apparatuses, a workpiece is cut at a predetermined angle θ, and thus a turning process is carried out on the workpiece. In the combined processing lathe disclosed in Japanese Laid-Open Patent Publication No. 2000-254802, for example, a tool which is placed in the direction perpendicular to the axis of the workpiece spindle is used to process the workpiece in order to avoid the effects of the thermal displacement of the workpiece spindle.
In the case where a turning process is carried out on the outer peripheral surface of a workpiece in the above described combined lathe apparatus having automatic tool replacing means, a problem arises that bending of the workpiece due to its own weight directly affects the process precision (cylindricity). In general, the amount of bending δ (mm) in a supported workpiece can be calculated in Formula (1).δ=(5·P·L3)/(384·E·I)  (1)
P is the weight of the workpiece (N), L is the length of the workpiece (mm), E is a modulus of direct elasticity (N/mm2), and I is the second moment of area (mm4). Formula (1) includes the cubed length L of the workpiece. Therefore the length L of the workpiece is very dominant over the amount of bending δ. Thus, the greater the length L of the workpiece is, the greater the amount of bending δ due to the weight of the workpiece becomes. Accordingly, when a turning process is carried out at a predetermined angle θ relative to the horizontal line Yt, it is subjected to the effects of the workpiece bending, and therefore the precision of processing the workpiece becomes poor (hereinafter this problem is referred to as first problem).
In terms of the general structure of the bed, the thickness in the vertical direction is small and the length in the lateral direction is great for the ease of use. In the case of a machine tool, the jack bolt is adjusted so that the machine tool is positioned. However, the location of the base changes and the load applied to the jack bolt also changes because of the occurrence of an earthquake, a change in the state of the base made of concrete on which the machine tool is installed and the like. Therefore the degree of bending in the vertical direction of the bed which is thin and has a low rigidity is easy to change in machine tools.
A change in the degree of bending in the vertical direction means the same as a change in pitching as shown in FIG. 15. Pitching means a deviation in the angle when the tool headstock moves along the axis of the workpiece spindle. The amount of bending δ is due to the workpiece W bending in the case where the error on the machine side is “0”, and the pitching is due to an error in the machine.
This error affects the position of the blade in the vertical direction and at the same time affects the precision of processing the workpiece W (hereinafter this problem is referred to as second problem). In the case where this problem is addressed by readjusting the jack bolt, a great amount of time and effort are required for the adjustment. In addition to this, it is difficult to determine whether or not the change in the state of the base has lowered the precision.
Furthermore, a rotating tool, a turning processing tool and the like are attached to the tool headstock in accordance with contents of processing. A motor for rotating the rotating tool, a bearing for supporting an object to be rotated and the like are incorporated in the tool headstock. In this case, the motor and the bearing are the heat source which causes a thermal displacement in the tool headstock. The thermal displacement is easily caused along the axis of the spindle of the tool. As shown in FIG. 14, the direction of the axis of the spindle of the tool coincides with the direction of cutting in which the workpiece is processed using a turning processing tool. That is to say, the turning processing tool is subjected to the effects of the thermal displacement in the tool headstock even after the rotating tool is replaced with the turning processing tool. In FIG. 14, Wa indicates the outer diameter of the workpiece W on which a cutting process has been carried out in such a state as to be subjected to thermal displacement. In FIG. 14, q indicates the length gained by subtracting the outer diameter Wa of the workpiece W on which a cutting process has been carried out in such a state as to be subjected to thermal displacement from the outer diameter of the workpiece W on which a cutting process has been carried out in such a state as not to be subjected to thermal displacement.
Accordingly, thermal displacement in the turning processing tool affects the precision of processing in an outer diameter turning process and the outer diameter of the workpiece W after processing (hereinafter this problem is referred to as third problem). A technology for allowing a machine to correct the amount of thermal displacement has been proposed. In accordance with this technology, however, no fundamental measure is taken against the problem and therefore it is difficult to stably carry out a turning process with high precision.
The combined processing lathe disclosed in Japanese Laid-Open Patent Publication No. 2000-254802 does not have an automatic tool replacing apparatus where a rotating tool and a turning processing tool can be replaced. Therefore, the first to third problems with combined process lathing apparatuses having an automatic tool replacing apparatus to which the present invention relates cannot be solved at the same time.